N-ethylmaleimide sensitive fusion protein (NSF) is a homohexameric ATPase necessary for a variety of vesicular and membrane fusion events in eukaryotic cells. NSF is known to be a hexamer of 83 kDa monomers, with each monomer being roughly divided into three equally sized domains-the N-terminal "N" domain, the middle "D1" ATPase domain, and the C-terminal "D2" ATPase domain. Domain N interacts with other proteins required for membrane fusion, D1 has ATPase activity necessary for fusion, and D2 binds ATP for oligomerization, and possibly links ATP hydrolysis to NSF recycling pathway(s) for NSF. Crystals of full-length NSF, the N domain, and the D2 domain have been produced. A very high resolution molecular structure of the D2 domain would provide valuable information: possible orientation of the monomers in the hexamer, a rare high resolution picture of this particular class of ATPase fold, and phase information in later studies of the full length crystals.